L-threonine, a kind of essential amino acid, is widely used as an additive to animal feed and food, and as fluids and synthetic materials for medical and pharmaceutical use. L-threonine is mainly produced by fermentation using Escherichia coli, Serratia, Providencia or Corynebacterium, developed by artificial mutation methods or gene recombination methods, or artificial mutant strains thereof. Genes related to the biosynthesis of threonine and various methods for increasing the expression of these genes have been developed, but the demand for a method capable of producing L-threonine in high yield in a more cost-effective manner still exists.
It is known that GalP protein that is encoded by galP in E. coli is galactose permease that transports a variety of monosaccharides, including galactose and glucose, into cells (V. Hernandez-Montalvo F. Valle F. Bolivar G. Gosset, Appl Microbiol Biotechnol (2001) 57:186-191). In addition, it is known that the GalP protein also acts as glucose permease (Venter, Henrietta et al., Biochemical Journal (2002) 363:243-252). It was reported that, when the expression of the galP gene in E. coli is increased, for example, by increasing the copy number of the gene, the production of threonine in the E. coli is increased (WO 2004/087937).
It was reported that inositol permease that is encoded by iolT1 and iolT2 genes in Corynebacterium glutamicum can also act as glucose permease (Ikeda et al., Appl Microbial Biotechnol (2011) 90:1443-1451). It was also reported that iolT1 and iolT2 genes have high homology with the galP gene of E. coli. However, the correlation between inositol permease and threonine production has not yet been reported.
The present inventors have found that, when iolT1 gene and/or iolT2 gene encoding inositol permease in microorganisms of the genus Corynebacterium is introduced into a microorganism of the Escherichia Coli, the microorganism of the genus Escherichia has enhanced L-threonine productivity, thereby completing the present invention.